Vehicles such as automobiles use a subframe structure fixed to a front side frame serving as a vehicle-body member, installed with a suspension component such as, e.g., a suspension arm and a stabilizer, and used for supporting the suspension component.
As a subframe structure of this type, Patent Literature 1, e.g., discloses one including a rear member made of light metal and installed with a suspension component; two side members made of steel, joined to the front ends of the two lateral sections of the rear member, and extending toward the front of a vehicle; and a cross member connecting the two side members to each other in the width direction of the vehicle.
In addition, Patent Literature 2 discloses a vehicle subframe in which a grid-shaped die-cast subframe is configured to be divided into two and the freedom degree of the shape of the dividing and joining portion can be enhanced.
Further, Patent Literature 3 relates to the joining mechanism of an automobile structure in connection with a center pillar and discloses the friction stir welding of a flange at an end edge on the side of the opening of a box-shaped structural member made of an aluminum alloy and a flat-plate-shaped cover made of a zinc steel plate.
Furthermore, Patent Literature 4 discloses a method for joining different types of metals together in which both materials made of the different types of metals are superposed one on the other via a sealant, the deformation resistance of the sealant is reduced by heating to discharge the sealant interposed at the joining section from the joining interface, and both the materials are joined together by resistance welding or laser beam irradiation in a state in which both the materials are brought into direct contact with each other. Furthermore, Patent Literature 5 describes a method for joining different types of metals together by friction welding.